1. Field of the Invention
The present invention relates to a driving device utilized in a scanner and a scanner having such driving device.
2. Description of the Related Art
A scanner having a main body, a scanning member, a belt, and a driving device is known. In such scanner, the scanning member is installed inside the main body. A tempered glass is disposed on the top surface of the main body above the scanning member. The driving device moves the scanning member by driving the belt.
FIG. 5 shows a typical type of a generally known driving device utilized in scanners. The driving device 100 includes a stepping motor 101, a metal frame 102, a motor shaft 103, and a pinion 104. The stepping motor 101 is fixed on the bottom surface of the frame 102, and the motor shaft 103 of the stepping motor 101 penetrates the frame 102. At the distal end of the motor shaft 103 protruding out on the top surface side of the frame 102, a pinion 104 is disposed.
The driving device 100 also includes a reduction gear 110. The reduction gear 110 includes a first gear 111 and a second gear 112. The diameter of the first gear 111 is larger than that of the second gear 112, and the first gear 111 and the second gear 112 are formed as one component, and thus they rotate together. The reduction gear 110 is rotatably supported on the top surface of the frame 102 in a manner that the first gear 111 is disposed in between the second gear 112 and the frame 102, and the first gear 111 is engaged with the pinion 104.
Further, the driving device 100 includes an interposing gear 120. The interposing gear 120 includes a third gear 121 and a pulley 122. The third gear 121 and the pulley 122 are formed as one component, and thus they rotate together. The interposing gear 120 is rotatably supported on the top surface of the frame 102 in a manner that the third gear 121 is disposed in between the pulley 122 and the frame 102, and the third gear 121 is engaged with the second gear 112 of the reduction gear 110.
Furthermore, a belt (not shown in the figure) is wound around the pulley 122 of the interposing gear 120.
When utilizing the driving device 100, a driving force generated by the stepping motor 101 is transmitted from the pinion 104 to the first gear 111 of the reduction gear 110, and then from the second gear 112 of the reduction gear 110 to the third gear 121 of the interposing gear 120. Finally, the driving force is transmitted from the pulley 122 of the interposing gear 120 onto the belt not shown in the figure. The belt is driven to move the scanning member.
The driving device 100 of FIG. 5 engages the second gear 112 of the reduction gear 110 and the third gear 121 of the interposing gear 120, while maintaining the pulley 122 higher than the other gears so as to secure the working liability for the process of winding the belt onto the pulley 122. This requires the interposing gear 120 to be supported on the frame 102 at certain distance therefrom. The shaft 123 for the interposing gear 120 must be elongated in the orthogonal direction with respect to the frame 102.
FIG. 6 shows another typical type of a generally known driving device utilized in scanners. The detailed description of the driving device 200 in common with the driving device 100 of FIG. 5 will be abridged. However, the driving device 200 in FIG. 6 differs widely from the driving device 100 in that the reduction gear 210 is rotatably supported on the top surface of the frame 102 in a manner that the second (smaller) gear 212 is disposed in between the first (larger) gear 211 and the frame 102.
With this driving device 200, similarly, a driving force generated by the stepping motor 201 is transmitted from the pinion 204 to the first gear 211 of the reduction gear 210, and then from the second gear 212 of the reduction gear 210 to the third gear 221 of the interposing gear 220. Finally, the driving force is transmitted from the pulley 222 of the interposing gear 220 onto a belt not shown in the figure.
The driving device 200 of FIG. 6 has the reduction gear 210 with the first (larger) gear 211 disposed above the second (smaller) gear 212. The pinion 204 is required to be engaged with the first gear 211, which is remote from the frame 202. For this reason, the motor shaft 203 is elongated in the orthogonal direction with respect to the frame 202.
Aside from the driving devices described above, a driving device including a motor and an interposing gear is known. As is taught in the Japanese Patent Application Publication No. 10-86475, such driving device further includes a pinion engaged with a third gear of an interposing gear.
The motor of the driving device described above has a motor shaft, on which a pinion is fixed. The pinion is disposed at the distal end of the motor shaft far from the frame. The motor shaft must be elongated in the orthogonal direction.
In the driving device 100 of FIG. 5, the shaft 123 is elongated. The shaft 123 trembles when the stepping motor 101 transmits the driving force onto the belt not shown in the figure. Also, in the driving device 200 of FIG. 6, the motor shaft 203 is elongated. The motor shaft 203 trembles when the stepping motor 201 transmits the driving force onto the belt not shown in the figure. In the driving device of the Japanese Patent Application Publication No. 10-86475, the motor shaft with the pinion disposed at the distal end is elongated. The motor shaft trembles when the motor transmits the driving force to the belt.
In all of the cases above, the trembling of the shaft is transmitted onto the belt. The trembling transmitted to the belt causes the movement of the scanning member to sway in an inappropriate direction. In such case, the scanning member cannot be moved precisely.
Furthermore, the driving device 100 of FIG. 5 has four height positions in the orthogonal direction with respect to the frame 102, that is, the direction parallel to the motor shaft 103 or the shafts of the reduction gear 110 and of the interposing gear 120. Such height position will be referred to as “level” in the description below. Hence, the driving device 100 has four levels: a level of which the stepping motor 101 is located, a level of which the pinion 104 and the first gear 111 of the reduction gear 110 are located, a level of which the second gear 112 of the reduction gear 110 and the third gear 121 of the interposing gear 120 are located, and a level of which the pulley 122 of the interposing gear 120 and the belt not shown in the figure are located. The four levels are stacked on top of each other, thus thickening the orthogonal space which the driving device 100 occupies when installed into the scanner.
The driving device 200 of FIG. 6 has three levels: a level of which the stepping motor 201 is located, a level of which the second gear 212 of the reduction gear 210 and the third gear 221 of the interposing gear 220 are located, and a level of which the pinion 204, the first gear 211 of the reduction gear 210, the pulley 222 of the interposing gear 220 and the belt not shown in the figure are located. The three levels are stacked on top of each other, again thickening the orthogonal space which the driving device 200 occupies when installed into the scanner.